Furan and its derivatives are useful precursors for industrial chemicals in the area of, for example, pharmaceuticals, herbicides and polymers. Furan can readily be converted into tetrahydrofuran (THF) and 1,4-butanediol (1,4-BDO), which are valuable chemicals used industrially as solvents and in the production of elastic fibres such as elastane/spandex, polybutyrate terephthalate and derivatives of gamma butyrolactone.
These chemicals are usually produced industrially via a number of routes from petrochemical feedstocks, obtainable from fossil fuels. One industrial route for the production of 1,4-BDO requires the reaction of acetylene with two equivalents of formaldehyde followed by hydrogenation of the resultant 1,4-butynediol to form 1,4-butanediol. In an alternative process, propylene oxide is converted to allyl alcohol. The allyl alcohol is then hydroformylated to form 4-hydroxybutyraldehyde, which may be hydrogenated to form 1,4-butanediol. Other traditional routes use butadiene, allyl acetate or succinic acid as starting materials.
1,4-butanediol may also be produced as a side-product in a method for making tetrahydrofuran (THF) by oxidizing n-butane to crude maleic anhydride followed by catalytic hydrogenation.
In recent years, increased efforts have focused on producing chemicals, including furan and its derivatives such as 1,4-BDO and THF, from renewable feedstocks, such as sugar-based materials.
A method for obtaining furan from non-fossil fuel based sources involves the decarbonylation of furfural. Examples of reaction processes for achieving this and the subsequent conversion of the furan into its derivatives can be found in Hoydonck, H. E., Van Rhijn, W. M., Van Rhijn, W., De Vos, D. E. & Jacobs, P. A. (2012) Furfural and Derivatives, in Ulmann's Encyclopedia of Industrial Chemistry (volume 16, pp 285-313), Wiley-VCH Verlag GmBH & Co. KGaA, Weinheim; Dunlop, A. P. and Peters, F. N., in The Furans Reinhold Publ. Co, 1953; K. J. Zeitsch, in “The Chemistry and Technology of Furfural and its Many By-products” Sugar Series 13, Elsevier, 2000; Lange, J-P, van der Heide, E, van Buijtenen, J., and Price, R.; Furfural-A Promising Platform for Lignocellulosic Biofuels; ChemSusChem 2012, 5, 150-166 and Watson, J. M., Ind. Eng. Chem. Prod. Res. Develop., 1973, 12(4), 310. Furfural may be obtained from hemicellulose via acid hydrolysis in the liquid phase as well as in the gas phase as described in WO 2002/22593 and WO 2012/041990.
The product stream from a reaction process including the decarbonylation of furfural will contain furan, carbon monoxide, hydrogen and other by-products. Carbon monoxide often acts as a poison to catalysts used in subsequent reactions to convert furan into THF and 1,4-BDO and should be removed from the product stream. This may be carried out by condensation of the furan after considerable compression and cooling of the stream comprising furan, CO and H2, for example to greater than 1.5 MPa and less than 20° C. However, due to the low boiling point of furan (31.3° C.), it is difficult to remove carbon monoxide from this mixture by distillation without substantial losses of furan.
It would, therefore, be advantageous to provide a method for the production of furan from furfural in which the furan may be separated from undesirable by-products, such as carbon monoxide, made in its production without significant losses of useful materials.